Do home painting contractors have to be certified in the state they work in?

It depends on the state. Some do require certification, others do not; however, at the least you will probably have to have Workmens Compensation Insurance and a Business License. Also, many General Contractors will require you to have a Liability Insurance policy.

Yes a contractor must be licensed and insured int he state in whihc they work. Otherwse you are not dealing with a contractor,only someone claiming to be.